Rotational molding is a single-surface molding process. This means that the mold can only affect the quality of one surface of the molded part. The advantage of rotational molding is that the wall thickness distribution of rotomolded parts can be controller relatively easily by changing the speeds of rotation of the mould about the two perpendicular axes. Its good to specify a minimum wall thickness rather than a nominal wall thickness. As there is very little melt flow in rotational molding, the speeds and speed ration during the rest of the cycle is not so critical.
A rotational moulding machine comprises an oven, at least one arm arranged, in use, to rotate a mould within and relative to oven. It has a connection portion for connecting mould to arm and a cabling receiving section for receiving cabling connected between outside of oven and connection portion. A first conduit portion for the flow therein of cooling fluid from outside of oven into oven towards connection portion, and a second conduit portion for the return flow there along of cooling fluid from inside of oven to outside of oven. It utilizes a pump for pumping cooling fluid through first and second conduit portions. The pumped flow of cooling fluid through first and second conduit portions serves to cool connection portion and/or cabling receiving section.